<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>模态框</title>
    <link href="../../../css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
    <div class="dropdown" id="mydropdown">
        <button class="btn btn-default" id="dLabel" type="button" data-toggle="dropdown">
                下拉菜单
            <span class="caret"></span>
        </button>
       <ul class="dropdown-menu" role="menu">
          <li>一y</li>
          <li>一y</li>
          <li>一y</li>
          <li>一y</li>
      </ul>
    </div>
    <script src="../../../js/jquery-2.1.1.js"></script>
    <script src="../../../js/bootstrap.js"></script>
    <script>
    $("#mydropdown").on("shown.bs.dropdown",function(e){
    alert("Hello");
    })
    </script>
</body>
</html>